Hearing Aid Microactuator

ABSTRACT

A fenestration piercing the otic capsule bone of the cochlea receives a therapeutic appliance, such as a microactuator, plug, micropump for drug or therapeutic agent delivery, electrode, and the like. Several different ways of achieving a ‘water tight’ seal between the otic capsule bone and the therapeutic appliance are provided. The therapeutic appliance may be implanted with or without a sheath or sleeve lining the wall of the fenestration formed using specialized surgical burrs. The burrs permit safely fenestrating the otic capsule bone adjacent to the scala tympani of the cochlea without damaging the basilar membrane or organ of corti. This approach may also be adopted for safely fenestrating other areas of the inner ear such as the scala vestibuli, bony labyrinth of semicircular canals, or walls of the vestibule, or the oval or round windows thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of co-pending U.S. patentapplication Ser. No. 10/494,345 filed Apr. 29, 2004, which is a NationalPhase of International Application No. PCT/US02/34360 filed Oct. 26,2002 which claims benefit of U.S. Provisional Patent Application Ser.No. 60/335,944 filed Oct. 30, 2001 and U.S. Provisional PatentApplication No. 60/409,514 filed Sep. 10, 2002 which are commonly ownedherewith.

TECHNICAL FIELD

The present invention relates to a fully implantable hearing aid system,and more particularly to devices and methods for mounting amicroactuator, or other therapeutic device, into a fenestration thatpierces the wall of the cochlea of a patient.

BACKGROUND ART

A biologically sealed attachment into the wall of the cochlea of apatient that is stable and watertight is often desired, not only for anacoustic actuator, but also for various other medical devices. U.S. Pat.No. 5,951,601 (“the '601 patent”) describes several methods forattaching a microactuator to a fenestration through the wall of thecochlea.

The invention disclosed in the '601 patent has several advantages. Acasing locates the hearing device very securely, without vibration. Inaddition, the invention makes the removal of the hearing device easy,should this be required. Thirdly, together with a precise atraumaticfenestration procedure it provides for a very precise microactuatorlocation, thereby ensuring that the microactuator is optimally situatedin the cochlea, without damage to the delicate structures of the innerear.

Specifically, the casing disclosed in the '601 patent receives amicroactuator of an implantable hearing aid system. The casing isimplanted into a fenestration that pierces the promontory of the oticcapsule bone. The promontory is a projection of the cochlea which is afluid-filled hearing portion of the inner ear. As described in the '601patent, the casing is adapted for receiving and attaching to the subjecteither a microactuator included in the implantable hearing aid system,or a dummy plug to replace the microactuator should removal of themicroactuator become necessary. Upon application of an electric signalto the microactuator, the microactuator directly stimulates fluid withinthe inner ear, which stimulation the subject perceives as sound.

A casing for attaching a microactuator of an implantable hearing aidsystem to a fenestration formed through a subject's promontory inaccordance with the disclosure of the '601 patent includes a sleeve thathas an outer surface. During implantation of the casing, a first end ofthe sleeve is received into the fenestration. Disposed in that location,the outer surface of the sleeve mates with the fenestration for securingthe casing within the fenestration. The hollow sleeve includes an innersurface adapted to receive a barrel of the microactuator.

The casing also includes a flange that is integral with the sleeve. Theflange projects outward from the outer surface of the sleeve about asecond end of the sleeve that is located distal from the first end. Theflange, through contact either with a mucosa that covers the promontoryor with the promontory itself, limits a depth to which the first end ofthe sleeve may enter into the fenestration.

A casing in accordance with the '601 patent may employ various means forsecuring the sleeve within the fenestration such as screwing into thepromontory or clamping to the promontory. Similarly, such a casing mayfasten the microactuator to the casing in various ways such as by athreaded attachment, with screws, with button-and-socket snap fasteners,or with a slotted tongue-and-groove lock. A casing in accordance withthe '601 patent may also include a keyway that receives a mating keyformed on the barrel of the microactuator for establishing anorientation of the implanted microactuator.

One difficulty in a process for securing a therapeutic appliance intothe wall of the cochlea is that the attachment be biologically sealed.Another difficulty in a process for securing a biologically sealedtherapeutic appliance into the wall of the cochlea is safelyfenestrating the otic capsule bone without damage to the membranouslabyrinth or organ of cord and thus, without damage to hearing.

DISCLOSURE OF INVENTION

An object of the present invention is to facilitate attachment of amicroactuator of an implantable hearing aid system or other therapeuticappliance, such as a microactuator, plug or micropump for drug ortherapeutic agent delivery, electrodes and the like, to a fenestrationformed through a subject's promontory, and to facilitate the therapeuticappliance's subsequent removal.

Another object of the present invention is to attach a microactuator ofan implantable hearing aid system or other therapeutic appliance, suchas a microactuator, plug or micropump for drug or therapeutic agentdelivery, electrodes and the like, to a fenestration formed through theotic capsule bone of a subject's cochlea.

Another object of the present invention is to provide an easilyimplanted casing for attaching a microactuator of an implantable hearingaid system to a fenestration formed through a subject's promontory.

Yet another object of the present invention is to provide surgical burrsthat permit safely fenestrating the otic capsule bone adjacent to thescala tympani of the cochlea without damage to the membranous labyrinthor organ of cord and thus, without damage to hearing.

Briefly, one aspect of the present invention relates to securing atherapeutic appliance, such as a microactuator, plug, micropump for drugor therapeutic agent delivery, electrodes, and the like, into afenestration that pierces the otic capsule bone of the cochlea. Thepresent invention includes several different ways of achieving a “watertight” seal between the otic capsule bone and the therapeutic appliance.The invention includes specific ways of implanting the therapeuticappliance both with and without a sheath lining the wall of thefenestration.

Another aspect of the present invention includes specialized surgicalburrs that enable the otologic surgeon to safely fenestrate the oticcapsule bone adjacent to the scala tympani of the cochlea without damageto the basilar membrane or organ of cordi. Utilizing the principles ofthe invention described herein, other areas of the inner ear may besafely fenestrated provided damage to the membranous labyrinth isavoided, e.g., fenestration of the scala vestibuli of cochlea, bonylabyrinth of semicircular canals, or walls of the vestibule. Theinvention disclosed herein might also be adopted for fenestration ofoval or round windows of the inner ear.

These and other features, objects and advantages will be understood orapparent to those of ordinary skill in the art from the followingdetailed description of the preferred embodiment as illustrated in thevarious drawing figures.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 schematically illustrates a fenestration that pierces thepromontory of the cochlea having been formed with fenestration burrswhich have precise, compound drilling diameters.

FIG. 2 shows a sectioned, prefabricated casing (sleeve) disposed in thefenestration that receives and secures a microactuator.

FIG. 3 shows how the sleeve may be coated on both sides with anelastomeric antibacterial material, thereby providing a very tightcompressive seal.

FIG. 4 shows interposition of an O-ring between the sleeve and themicroactuator.

FIG. 5 illustrates application of sealing rings of silastic or similarbiocompatible material to the sleeve and/or microactuator.

FIG. 6 shows a plug with an expandable bladder for fixation.

FIG. 7 schematically illustrates how the sleeve may be used with a fullyelastomeric plug for delivering a therapeutic agent into the cochlea.

FIG. 8 schematically illustrates how the sleeve may be used with anelastomeric plug and a cochlear electrode implant cable.

FIG. 9 illustrates a elastomeric plug with protruding ring.

FIGS. 10 and 11 schematically illustrate elastomeric plugs inserted intoa fenestration and lacking any sleeve.

FIGS. 12 a and 12 b illustrate fenestration burrs.

FIG. 13 shows a grooved fenestration for anchoring a microactuator.

FIG. 14 a shows one type of drill that may be used to make a groove intothe wall of the fenestration.

FIG. 14 b shows another type of drill that may be used to make a grooveinto the wall of the fenestration.

FIG. 15 shows the microactuator having protruding elastomeric rings tofit into the grooves.

FIG. 16 is a cross-sectional view of a sleeve illustrating elastomericrings applied thereto to fit into the grooves.

FIG. 17 shows locations for frequency maxima along a basil coil locatedwithin the cochlea, and displacement of the locations for frequencymaxima after treatment of the basilar membrane.

DESCRIPTION OF EXAMPLE EMBODIMENTS

FIG. 1 depicts a promontory wall 32 of a cochlea 34 that, in accordancewith the present invention, is pierced by a fenestration 36. An upperportion of a bony labyrinth within the cochlea 34 is called the scalavestibuli 42, while a lower portion of the bony labyrinth is called thescala tympani 44. A membranous labyrinth within the cochlea 34, calledthe scala media 46, lies between the scala vestibuli 42 and scalatympani 44. A “vestibular membrane,” called Reissner's membrane 48,separates the scala media 46 from the scala vestibuli 42, while abasilar membrane 52 separates the scala media 46 from the scala tympani44. A stria vascularis 54 and spiral ligament 56 are juxtaposed with aninner surface of the promontory wall 32.

FIG. 1 also illustrates how precise location of the fenestration 36 mayadvantageously position a microactuator with great precision in thecochlea 34. Preferably, the cylindrically-shaped fenestration 36includes two precision sections, an outer section 62 having a largerdiameter, and an inner section 64 having a diameter that is smaller thanthat of the outer section 62. The outer section 62 of the fenestration36 may be called a well 66. The fenestration 36 includes anannularly-shaped well floor 68 which spans between one edge of the outersection 62 and one edge of the inner section 64. Configured in this way,the fenestration 36 provides a space such that a microactuator may beintroduced into the scala tympani 44 for stimulating the basilarmembrane 52.

As illustrated in FIG. 2, after the fenestration 36 has been formedthrough the promontory wall 32 a unitary, i.e. one piece, sleeve 72 maybe inserted and fixed firmly within the promontory wall 32 of thecochlea 34. Generally it is desirable that over time the sleeve 72attach itself permanently to the promontory wall 32. The sleeve 72 maybe slit to ease introduction into the fenestration 36, but it should fittightly after being inserted. The sleeve 72 is preferably made out ofvery thin titanium e.g. a few mils thick (1 to 10 mils), althoughelastomeric sleeves may also be used. As described in the '601 patent,the sleeve 72 also preferably includes pre-located keyways 74 forreceiving corresponding keys 76 that extend from a microactuator 78. Thesleeve 72 with its keyways 74 and the keys 76 permit locking themicroactuator 78 in place by inserting the microactuator 78 into thetitanium sleeve 72 and rotating it 10° with a very small twist or snapaction. Thus, the sleeve 72 precisely locates of the microactuator 78both laterally and transversely. In this way the microactuator 78attaches to the sleeve 72 by a method similar to locking a cap on achildproof prescription bottle.

Complete hermetic sealing of the sleeve 72 and the microactuator 78 tothe promontory wall 32 is usually accomplished by the body itself. Theendothelial lining of the inner ear and the mucosal lining of the innerear will migrate across a biocompatible membrane, sealing the sleeve 72,microactuator 78 and the fenestration 36, similar to what occurs withthe prosthesis following stapedectomy (i.e. fenestration of the stapes).

To improve on the physical and biological sealing while this processoccurs, as depicted in FIG. 3 a biocompatible elastomeric coating 82 maybe applied both on both inside and outside walls of the titanium sleeve72. The coatings 82 act as a washer that improves the sealing and fitwhen the microactuator 78 is inserted into the sleeve 72. The coatings82 may be impregnated with an antibacterial agent, to imbue the sleeve72 with prophylactic properties.

Alternatively, as depicted in FIG. 4 an O-ring 84 may be interposedbetween a floor wall 86 of the sleeve 72 and a shelf 87 of themicroactuator 78 to provide a totally leak free seal. The coating 82 maystill be applied to the outside of the sleeve 72 to provide a tight sealwith the surrounding promontory wall 32. Similar to the coating 82, theO-ring 84 may likewise be impregnated with a prophylactic compound.

FIG. 5 depicts applying a ring 88 of silastic, Teflon, polyethylene, amaterial which expands upon hydration, or similar biocompatible materialalong the floor wall 86 of the titanium sleeve 72 and/or the shelf 87 ofthe microactuator 78. The rings 88 provide a “water tight” seal betweenthe microactuator 78 and the sleeve 72, and also to act as a “spring” toallow compression and rotation of the microactuator 78 as it is “locked”and thus held in place within the sleeve 72.

Alternatively, a pneumatically or hydraulically expandable bladder 91,surrounding either the sleeve 72 or the microactuator 78 or both, may beused for sealing the microactuator 78 within the promontory wall 32. Asdepicted in FIG. 6, expanding the bladder 91, either pneumatically orhydraulically, tightly seals the microactuator 78 to sleeve 72.

The system described thus far consists of a metal sleeve, accepting ametal body which attaches securely and positively to the former. Thisfenestration 36 and the sleeve 72 secured therein locate themicroactuator 78 precisely in the cochlea 34. Alternatively, it ispossible to replace the metal body of the microactuator 78 with a plugmade from a soft material that fits in the sleeve 72, and which may beheld there by elastic pressure. Under these conditions, the sleeve 72still provides good lateral positioning for the plug, and can also stillprovide good transverse location, such that the plug does not penetratefurther into the cochlea 34 than desired. Such a soft plug may often bedesired when the insert is only temporary, e.g. if the plug is used fordelivering a therapeutic agent into the cochlea 34.

In another application for the titanium sleeve 72, a micropump can besecurely attached to the titanium sleeve 72 in the fenestration 36 todeliver precisely measured doses of medication directly into the innerear. This drug delivery system may be shaped similar to themicroactuator 78, and enclose a therapeutic agent reservoir right atthis location (i.e. for very small volume delivery). The micropump couldcontain the necessary reservoir of medication when only tiny amounts(microliters) will be delivered from a pulsed piezo-electric mechanismat intervals.

If a larger reservoir of medication is required, a hermetically sealedcontainer made from biocompatible materials (e.g., titanium) may beimplanted in the mastoid cavity or subcutaneously. The reservoir isconnected to the implanted micropump by hollow tubing extending from themastoid cavity through the facial recess to a dispensing plug located inthe sleeve 72 at the cochlea 34. The micropump is connected to aprogrammable signal processor and battery implanted either in themastoid cavity or subcutaneously with leads extending through the facialrecess or antrum. The micropump would be activated by telemetry eitherfor single dose or by signal processor programmed by telemetry to adjustthe dosage and frequency of medication delivery to the inner ear. Thesubcutaneous reservoir may be periodically refilled by transcutaneousinjection utilizing sterile techniques.

For example, if the drug reservoir is located away from the inner ear, acapillary connection may be made directly to a plug. In the illustrationof FIG. 7, the titanium sleeve 72 holds a soft elastomeric plug 92 whichreceives one end of a capillary 94. The other end of the capillary 94connects to a reservoir 96 that holds a therapeutic agent. The soft plug92 itself may contain prophylactic agents, for example to guard againstinfection.

FIG. 8 depicts this same approach as applied for introducing a cochlearimplant electrode cable 102 into the cochlea 34. The cochlear implantelectrode cable 102 passes through a hole 104 in the elastomeric plug92. When disposed within the cochlea 34, the cochlear implant electrodecable 102 is free to move until the plug 92 is pressed into place in thesleeve 72. Upon pressing the plug 92 into the sleeve 72, the hole 104closes around and circumferentially clamps the cochlear implantelectrode cable 102. Though not illustrated in FIG. 8, the soft plug 92may be tapered or double tapered to provide a good friction fit to thesleeve 72. Hence the structure schematically illustrated in FIG. 8provides a leak-tight, bacteria-free seal.

As illustrated in FIG. 9, to provide safe anchoring of the soft plug 92,it may be encircled by a raised ring 112 that is adapted to fit into acorresponding outwardly projecting groove 114 that encircles the sleeve72. Radial compression of the plug 92 upon insertion into the sleeve 72squeezes the hole 104 to thereby fix any object passing therethroughsuch as the capillary 94 or the cochlear implant electrode cable 102which was free to move for adjustment before insertion of the soft plug92. Even a hard plug 92 may also be attached this way to the sleeve 72.

Finally, FIGS. 10 and 11 illustrate that, for some applications, it isalso possible to omit the sleeve 72 altogether; i.e. no sleeve 72 ispresent. Those elements depicted in FIGS. 10 and 11 that are common tothe structures illustrated in FIGS. 1-9 carry the same reference numeraldistinguished by a prime (“′”) designation. In FIG. 10, the compressivebiocompatible elastic plug 92′, used with a remote drug delivery systemhaving a reservoir 96′, is simply squeezed into the fenestration 36′that pierces the promontory wall 32′. FIG. 11 shows a similar plug 92′used with a cochlear implant electrode cable 102′, forced with the plug92′ against the fenestrated promontory wall 32′. As stated previously,the plug 92′ depicted in FIGS. 10 and 11 may contain antibacterialcompounds for prophylactic action. In either instance illustrated byFIGS. 10 and 11, an expanding re-entrant bladder may be used to provideanother way of clamping the plug 92′. Note that the system can again bedesigned such that the compression upon insertion will fix the cochlearimplant electrode cable 102′, which is free to move until the plug 92′is inserted into the promontory wall 32′.

Forming the fenestration 36 into the promontory wall 32 of the cochlea34 or other area of the otic capsule bone as depicted in FIG. 1 issafely performed with guarded fenestration burrs 122 and 124 depictedrespectively in FIGS. 12 a and 12 b. The unitary, i.e. one piece,fenestration burrs 122 and 124 of the present invention permit forming aprecise 1.4 mm diameter inner section 64 of the fenestration 36 and a1.8 mm diameter well 66 in the promontory wall 32 of the cochlea 34 asillustrated in FIG. 1. The fenestration burrs 122 and 124 respectivelyattach to a conventional, low frequency microdrill (<2000 rpm), e.g.Synergy stapes hand piece, for rotating the fenestration burrs 122 and124 during formation of the fenestration 36. Since the microdrill isconventional, it is not illustrated in any of the figures. An elongatedshaft 128 of each of the fenestration burrs 122 and 124, with respect towhich all diameters specified below for the fenestration burrs 122 and124 are measured, can be readily adapted for use with any selected oneof several commercially available ear microdrills. The fenestrationburrs 122 and 124 are guarded to limit penetration into scala tympani 44and thus, avoid injury to the structures of cochlea 34 illustrated inFIG. 1. Flutes on the fenestration burrs 122 and 124 are configured todischarge bone dust away from the cochlea.

The initial fenestration burr 122 illustrated in FIG. 12 a hasdimensions that are based on the thickness of the promontory wall 32 atthe proposed fenestration site measured in 12 human cochleae. Theinitial fenestration burr 122 includes a cutting burr 132 that is 1.4 mmin diameter and is located at a distal end of the shaft 128 furthestfrom the microdrill. A second, cylindrically-shaped polishing burr 134is located along the shaft 128 near, e.g. 0.5 mm, from the cutting burr132 and formed concentrically on the shaft 128 with the cutting burr132. The polishing burr 134 is diamond studded, is 1.8 mm in diameterand extends 0.5 mm along the shaft 128 from a washer-shaped flange orcollar 136 that is formed concentrically on the shaft 128 with thecutting burr 132 and the polishing burr 134. During use, the polishingburr 134 drills a 0.5 mm deep well 66, i.e. the outer section 62, in thepromontory wall 32 of the cochlea 34 while the cutting burr 132 beginsforming the smaller diameter inner section 64 of the fenestration 36.The collar 136, which is 2.0 mm in diameter and is juxtaposed with aside of the polishing burr 134 furthest from the cutting burr 132,contacts an outer surface of the promontory wall 32 to limit penetrationof the initial fenestration burr 122 thereinto.

A sequence of five (5) subsequent fenestration polishing burrs 124,illustrated by the fenestration polishing burr 124 in FIG. 12 b, areused to complete penetration of the promontory wall 32 and formation ofthe inner section 64 of the fenestration 36. Each of the fenestrationpolishing burrs 124 includes a polishing burr 142 that is 1.4 mm indiameter. The each of fenestration polishing burrs 124 also includes aprotective washer-shaped collar 146 that is located a short distancefrom the polishing burr 142 as indicated by an arrow 144 in FIG. 12 b,and formed concentrically on the shaft 128 with the polishing burr 142.The distal end of the polishing burrs 142 in the sequence offenestration polishing burrs 124 respectively extend a distance furtherand further from the collar 146. Preferably the distal end of polishingburr 142 in the sequence of fenestration polishing burrs 124 extendsrespectively 0.75 mm, 1.00 mm, 1.25 mm, 1.50 mm and 1.75 mm from thecollar 146. The collar 146 measures 1.8 mm diameter and reaches to awell floor 68 of the well 66, thus centering the polishing burr 142 aswell as limiting its penetration.

A microactuator, micropump, electrode or similar device may be attachedin the following way to the fenestration 36 in the promontory wall 32 ofthe cochlea 34 or other area of the otic capsule without the sleeve 72lining the fenestration 36. First the fenestration 36 is safely formedin the promontory wall 32 of the cochlea 34 or other area of the oticcapsule using the guarded fenestration burrs 122 and 124 depicted inFIGS. 12 a and 12 b and described above. Next, as depicted in FIG. 13,circumferential grooves 152 and 154 (e.g. 0.10-0.15 mm in depth) aredrilled into the bony wall surrounding the fenestration 36 respectivelyencircling the outer section 62 and the inner section 64 at precisedistances respectively below and above the well floor 68 of the well 66.In certain instances a single groove 152 or 154 may be sufficient forthe intended purpose. The grooves 152 and 154 can be precisely formed asdescribed below using fenestration grooving burrs 162 and 164 depictedrespectively in FIGS. 14 a and 14 b.

Each of the unitary, i.e. one piece, fenestration grooving burrs 162 and164 includes an elongated shaft 166 similar to the shaft 128 of thefenestration burrs 122 and 124 depicted respectively in FIGS. 12 a and12 b. Similar to the fenestration burrs 122 and 124, the fenestrationgrooving burrs 162 and 164 also respectively attach to a conventional,low frequency microdrill (<2000 rpm) that is not illustrated in any ofthe figures. Each of the fenestration grooving burrs 162 and 164 alsoincludes a washer-shaped collar 168. Each collar 168 is slightly largerthan the diameter of the inner section 64 of the fenestration 36depicted in FIG. 1 (e.g. 1.5 mm diameter), but smaller than the diameterof the well 66. Such a diameter for the collar 168 permits resting thecollar 168 on the well floor 68 of the well 66 when drilling the groove152 or 154, but allowing movement of the fenestration grooving burr 162or 165 laterally, eccentrically 360° around the circumference of thefenestration during drilling.

The fenestration grooving burr 162 depicted in FIG. 14 a also includes acutting wheel 172 that is located at a distal end of the shaft 166 ashort distance from the collar 168 and formed concentrically on theshaft 166 with the collar 168. If the inner section 64 has a diameter of1.4 mm, the well 66 has a diameter of 1.8 mm and the collar 168 has adiameter of 1.4 mm, a 1.4 mm diameter for the cutting wheel 172 permitsdrilling 0.15 mm deep groove 154 circumferentially in the inner section64 of the fenestration 36 at a precise distance below the well floor 68of the well 66. The depth of the groove 154 drilled by the fenestrationgrooving burr 162 is controlled by the difference in diameters betweenthe collar 168 and the cutting wheel 172, and between the inner section64 and the well 66.

The fenestration grooving burr 164 depicted in FIG. 14 b includes thecollar 168 that is located at a distal end of the shaft 166 and acutting wheel 176 that is located along the shaft 166 a short distancefrom collar 168 and formed concentrically on the shaft 166 with thecollar 168. The fenestration grooving burr 164 can be used to make thegroove 152 above the well 66 of the well 66. Again, during formation ofthe groove 152 the collar 168 rests on the well 66 of the well 66. Ifthe well 66 has a diameter of 1.8 mm and the collar 168 a diameter of1.5 mm, a 1.8 mm diameter for the cutting wheel 176, i.e. equal to thediameter of the well 66, produces a 0.15 mm deep groove 152 in thepromontory wall 32 surrounding the well 66 a precise distance above thewell floor 68 of the well 66.

Installation of the microactuator 78, micropump or cochlear implantelectrode cable 102, etc. into the fenestration 36 depicted in FIG. 13can be stabilized in the following way. As depicted in FIG. 15, one ormore rings 182 and 184 of pliable material are permanently attachedaround the microactuator 78 at appropriate locations along themicroactuator 78. Upon inserting the microactuator 78 into thefenestration 36 depicted in FIG. 13, the rings 182 and 184 compress andthen expand into the corresponding grooves 152 and 154 as themicroactuator 78 reaches the proper depth thereby fixing themicroactuator 78 in the grooves 152 and 154. Similar to the ring 88depicted in FIG. 5, several different biocompatible materials may beused for the rings 182 and 184, including silastic, Teflon,polyethylene, a material which expands upon hydration, or similarbiocompatible material. As described above, this method for attachingthe microactuator 78 to the grooved fenestration 36 avoids any need forthe sleeve 72 to line the fenestration 36. Similar to the coating 82depicted in FIG. 3 and the O-ring 84 depicted in FIG. 4, if beneficialthe rings 182 and 184 may be impregnated with prophylactic material.

A ring 186 of pliable biocompatible material may also be applied aroundthe distal end of the microactuator 78 or other device to expand uponreaching the lumen of the cochlea 34, e.g. scala tympani 44 or scalavestibuli 42. Use of the ring 186 may avoid any need for grooving thewall of the fenestration 36, but requires that the fenestration 36 havea precise, pre-established depth.

As best illustrated in FIG. 15, the microactuator 78 includes an outerbarrel 192 which abuts the annularly-shaped shelf 87 along a circularcommon edge 194. During implantation of the microactuator 78 directlyinto the fenestration 36, the outer barrel 192 is inserted into andbecomes fixed firmly in the outer section 62, and the shelf 87 to bejuxtaposed with the well floor 68 of the fenestration 36. Themicroactuator 78 also includes an inner barrel 196 which projects awayfrom the outer barrel 192 and abuts the common edge 194 along a circularcommon edge 198. During implantation of the microactuator 78 directlyinto the fenestration 36, the inner barrel 196 is inserted into andbecomes fixed firmly into the inner section 64.

As depicted in FIG. 16, in those instances in which the sleeve 72 isdesired so the microactuator 78 or other device may be easily removed,the rings 182 and 184 and/or ring 186 are applied abound the sleeve 72rather than the microactuator 78 so the sleeve 72 may be inserted andheld in place within the fenestration 36 similar to the microactuator 78depicted in FIG. 15. As depicted in FIG. 16, a thin layer 202 ofsilastic, Teflon, polyethylene, a material which expands upon hydration,or similar biocompatible material may also be applied to coat the floorwall 86 of the sleeve 72, and/or an optional flange 204 that is locatedat the top of the titanium sleeve 72. The thin layers 202 provide awater tight seal between the microactuator 78 or other device and thesleeve 72, and also act as a spring that allows compression and motionof the microactuator 78 as it is locked and then held in place withinthe sleeve 72. Similar methods may be used for fixing a micropump,electrode, or combination microactuator and electrode in thefenestration 36.

As best illustrated in FIGS. 16 and 2, the sleeve 72 includes an outerwall 212 which abuts the annularly-shaped floor wall 86 along a circularcommon edge 214. During implantation of the sleeve 72 into thefenestration 36, the outer wall 212 is inserted into and becomes fixedfirmly in the outer section 62, and the floor wall 86 becomes juxtaposedwith the well floor 68 of the fenestration 36. The sleeve 72 alsoincludes an inner wall 216 which projects away from the outer wall 212and abuts the common edge 214 along a circular common edge 218. Duringimplantation of the sleeve 72 into the fenestration 36, the inner wall216 is inserted into and becomes fixed firmly into the inner section 64.Implantation of the microactuator 78 into the sleeve 72 causes the outerbarrel 192 to be inserted into and fixed firmly in the outer wall 212,and the shelf 87 to be juxtaposed with the floor wall 86 of the sleeve72. Correspondingly, implantation of the microactuator 78 into thesleeve 72 also causes the inner barrel 196 to be inserted into a fixedfirmly into the inner wall 216.

The most common type of sensorineural hearing loss is decreasedsensitivity to high frequency sound caused by aging, noise exposure,diabetes, oto-toxicity, impaired blood supply to the inner ear, etc.High frequency hearing loss results from a deterioration of hair cellsin a basal coil 222 of the cochlea 34. Because of the complicated natureof haircells, they do not regenerate.

The cochlea 34 acts as a frequency analyzer, with the traveling wavereaching a maximum at various locations along the basilar membrane 52.The high frequency maxima occur in the basal coil 222 of the cochlea 34near the stapes, and the low frequency maxima near the apex due to thestiffness gradient of the basilar membrane 52. This separation of maximaalong the basal coil 222 is schematically illustrated in FIG. 17, whichshows the location of the various frequency maxima along the basilarmembrane 52.

If a therapeutic agent or procedure is introduced into the cochlea 34such that the basilar membrane 52 is made stiffer or its motion in thebasal coil 222 of the cochlea 34 blocked, the traveling wave of basilarmembrane displacement will move towards the apex of the cochlea 34depicted in FIG. 17. For example, the location of maximum displacementfor 10 kHz sound could be moved along the basal coil 222 to the locationthat previously sensed 2 kHz sound, the location of maximum displacementfor 5 kHz might be moved to the area previously stimulated by 1 kHz etc.

If the basal coil 222 of scala media 46 has no viable hair cells fromits most proximal point near the round window to the mid turn of thebasal coil 222, then the basal coil 222 would not produce nerve impulsesfor high frequencies, e.g. 10 kHz through 4 kHz, and thus would beinsensitive (“deaf”) to these frequencies. Movement of the travelingwave apically (i.e. towards the apex) along the basilar membrane 52 to alocation where hair cells are still present would now permitdepolarization of those hair cells thereby converting the sound intonerve impulses. In this way intact haircells are all used to the maximumextent possible to cover the entire frequency range.

Computer simulation studies and mechanical models of the cochlea 34indicate that if the traveling wave is moved apically the wave envelopeis compressed but still the “phase/time” analysis performed by thetraveling wave is maintained in this compressed state. Clinical studiesfrom electrical stimulation of the cochlea 34 with cochlear implantsconfirm that the brain can be retrained to interpret these new auditorymessages, and speech discrimination is possible. In essence, by movingthe traveling wave apically in a subject who has no surviving hair cellsin the basal coil 222 permits stimulating the remaining hair cells withhigh frequencies thereby allowing them to “volley” in synchrony with thehigh frequencies. Neuro-physiologic studies confirm that hair cellsthroughout the cochlea 34 have similar depolarization/repolarizationcharacteristics and thus theoretically are capable of synchronousdepolarization at frequencies from 100 to 20 kHz throughout the cochlea34.

Hearing sensitivity of the cochlea 34 is measured by pure tone thresholdbone conduction audiometric studies, which stimulate the fluid withinthe cochlea 34 directly. High frequency nerve loss implies a loss ofhair cells in the basal coil 222 of the cochlea 34. Because the locationof frequency maxima along the basilar membrane 52 is well known, theamount of transposition of the traveling wave to areas where hair cellsare intact can be determined by bone conduction audiometry. Thetreatment of the basilar membrane 52 would then be adapted so that therequired basilar membrane stiffening or restriction of its motion isaffected to that degree required for correctly projecting sound atspecific frequencies onto the remaining part of the basal membrane whichhas intact hair cells.

Stiffening the basilar membrane 52 could be accomplished with atherapeutic agent such as a drug, a cell regrowth factor, or any factorthat reduces or stiffens the elasticity of the basilar membrane 52. Analternative method is to obstruct the motion of the basilar membrane 52in the scala tympani 44 by physically limiting its downward motion witha bio-compatible material which would completely obstruct scala tympani44 in the basal coil 222 to the desired length of the cochlea 34. Thiswould require creating a new round window in the scala tympani distal tothe point of obstruction if sound vibrations are to enter the cochlea 34through the oval window. Conversely, a microactuator could be attachedto the distal end of the material obstructing the scala tympani 44, andsound introduced directly into scala tympani 44. In this scenario, theoval window would provide the necessary hydraulic decompression topermit the traveling wave of pressure and displacement withoutsignificantly increasing fluid impedance. It is recognized because ofthe impedance mismatching of the basilar membrane 52 that greater energywill be necessary to displace the basilar membrane 52 with thisobstructing technique. Again the traveling wave envelope will becompressed in both the horizontal and vertical planes.

INDUSTRIAL APPLICABILITY

In general, many if not all of the methods depicted in FIGS. 3 through11 and described above can be used when attaching a microactuator, amicropump, capillary, electrode, or combination microactuator/electrodeinto a fenestration 36 that pierces the wall of the cochlea 34.

Using structures such as those depicted in FIGS. 7 and 10, it isanticipated that conditions such as vertigo, tinnitus, suddensensorineural hearing loss, endolymphatic hydrops (Meniere's disease),autoimmune inner ear disease, and serous or viral labyrinthitis could beimproved by carefully perfusing measured doses of a variety ofmedications (e.g. steroids, a medication to suppress tinnitus, amedication to alter electrolyte balance in perilymph or endolymph,vasodilators, immune suppressants, anticoagulants, antibiotics,antiviral agents, plasma expanders, antioxidants, etc.) directly intothe inner ear. Research has recently discovered that hair cells in thecochlea 34 and vestibular labyrinth of some vertebrates have the abilityto regenerate. The micropump can perfuse a substance (e.g.,neurohormone, hair cell DNA actuator, Mathl or other gene therapy toenhance hair cell growth factor to encourage efferent nerve growth) intothe inner ear to stimulate regrowth of hair cells in the cochlea 34 inpatients with sensorineural hearing loss or repair damaged vestibularhair cells.

Another use for this invention depicted in FIGS. 8 and 11 is introducingan electrode into the inner ear and securely attaching it to the bonywalls of the promontory wall 32. In addition to fixing the cochlearimplant electrode cable 102 into the cochlea 34, application of low doseelectrical current can depolarize hair cells or neurons and may somedaybe used to relieve tinnitus or vertigo triggered by irritable peripheralhair cells or afferent neurons.

In each of the applications described above, attaching themicroactuator, micropump, or electrode to the titanium sleeve 72 liningthe fenestration 36 enables the surgeon to remove the device withminimal risk of damage to the inner ear. A new device can be inserted toreplace an existing one, or an existing device may be replaced by a“plug” if the device is no longer needed.

Although the present invention has been described in terms of thepresently preferred embodiment, it is to be understood that suchdisclosure is purely illustrative and is not to be interpreted aslimiting. Consequently, without departing from the spirit and scope ofthe invention, various alterations, modifications, and/or alternativeapplications of the invention will, no doubt, be suggested to thoseskilled in the art after having read the preceding disclosure.Accordingly, it is intended that the following claims be interpreted asencompassing all alterations, modifications, or alternative applicationsas fall within the true spirit and scope of the invention.

1. A therapeutic appliance configured for insertion into acylindrically-shaped fenestration that pierces a wall of a cochlea of asubject, the therapeutic appliance comprising: an outer barrelconfigured to be disposed at a distal end of the wall of the cochlea andconfigured to be inserted into and firmly fixed in a corresponding outerportion of the cylindrically-shaped fenestration, the outer barrelhaving an outer diameter dimension along a longitudinal axis; and aninner barrel configured to be disposed at a proximal end of the wall ofthe cochlea closest to the scala tympani region of the cochlea andopposite to the distal end, the inner barrel coupled to the outer barreland extending away from the outer barrel along the longitudinal axistoward the proximal end, the inner barrel having an inner barreldiameter dimension about the longitudinal axis, wherein the inner barreldiameter dimension is smaller than the outer barrel diameter dimension,the inner barrel configured to be inserted into and to be firmly fixedin a corresponding inner portion of the fenestration adjacent to theouter portion of the fenestration.
 2. The therapeutic appliance of claim1 wherein the therapeutic appliance includes a microactuator.
 3. Thetherapeutic appliance of claim 1 wherein the therapeutic applianceincludes a micropump.
 4. The therapeutic appliance of claim 1 wherein asleeve is positioned between the fenestration and the therapeuticappliance such that the inner barrel is in contact with a first circulararea of the sleeve having a first sleeve diameter dimensioncorresponding to the inner barrel diameter dimension and the outerbarrel is in contact with a second circular area of the sleeve having asecond sleeve diameter dimension corresponding with the outer barreldiameter dimension.
 5. The therapeutic appliance of claim 4, furthercomprising: an annularly-shaped shelf positioned between the innerbarrel and the outer barrel, the shelf having a shelf diameter dimensionless than the outer barrel diameter dimension and greater than the innerbarrel diameter dimension.
 6. The therapeutic appliance of claim 1,further comprising: an annularly-shaped shelf positioned between theinner barrel and the outer barrel, the shelf having a shelf diameterdimension less than the outer barrel diameter dimension and greater thanthe inner barrel diameter dimension.
 7. The therapeutic appliance ofclaim 4, further comprising: a biocompatible elastomeric coatingdisposed on an outer surface of the therapeutic appliance, the coatingfor effecting a seal between the outer surface of the therapeuticappliance and the sleeve.
 8. The therapeutic appliance of claim 4,further comprising: an expandable bladder configured to be interposedbetween the therapeutic appliance and the sleeve for effecting a sealtherebetween.
 9. The therapeutic appliance of claim 4, wherein the outerbarrel of the therapeutic appliance is encircled by at least one ringthat is configured to mate with and engage a corresponding groove of thesleeve.
 10. The therapeutic appliance of claim 4, wherein the innerbarrel of the therapeutic appliance is encircled by at least one ringthat is configured to mate with and engage a corresponding groove of thesleeve.
 11. The therapeutic appliance of claim 5, further comprising: anO-ring disposed on an outer surface of the shelf of the therapeuticappliance for effecting a seal between the sleeve and the shelf.
 12. Atherapeutic appliance configured for implantation into acylindrically-shaped fenestration that pierces a wall of a cochlea of asubject, the fenestration including an outer section and an innersection which is smaller in diameter than the outer section, thefenestration also including an annularly-shaped well floor that spansbetween one edge of the outer section of the fenestration and one edgeof the inner section thereof, the therapeutic appliance comprising: anouter barrel configured to be inserted into and firmly fixed in theouter section of the fenestration at a distal end, the outer barrelhaving a outer barrel diameter dimension about a longitudinal axis; anannularly-shaped shelf configured to be disposed within the wall of thecochlea, the annularly-shaped shelf coaxial with and adjacent to theouter barrel along the longitudinal axis, the shelf having an outer edgewhich abuts with an edge of the outer barrel and having a shelf diameterdimension about the longitudinal axis, wherein the shelf diameterdimension is smaller than the outer barrel diameter dimension, the shelfconfigured to be juxtaposed with the well floor of the fenestration uponinsertion of the therapeutic appliance fully into the outer section ofthe fenestration; and an inner barrel configured to be disposed at aproximal end closest to the scala tympani region of the cochlea andopposite to the distal end, the inner barrel coaxial with the shelf andthe outer barrel along the longitudinal axis, the inner barrel having aninner barrel diameter dimension about the longitudinal axis, wherein theinner barrel diameter dimension is smaller than the shelf and outerbarrel diameter dimensions, the inner barrel having an edge which abutswith an inner edge of the shelf and projects away from the outer barrelof the therapeutic appliance, the inner barrel configured to be insertedinto and firmly fixed into the inner section of the fenestration incommunication with the scala tympani region.
 13. The therapeuticappliance of claim 12, wherein the therapeutic appliance includes amicroactuator.
 14. The therapeutic appliance of claim 12, wherein thetherapeutic appliance includes a micropump.
 15. The therapeuticappliance of claim 12, wherein the outer barrel and the inner barrel arerespectively encircled by at least one ring of pliable material.
 16. Thetherapeutic appliance of claim 12, further comprising: a biocompatibleelastomeric coating disposed on an outer surface of the therapeuticappliance, the coating for effecting a seal between the outer surface ofthe therapeutic appliance and a sleeve engaged with the fenestration.17. The therapeutic appliance of claim 12, further comprising: an O-ringdisposed on an outer surface of the shelf of the therapeutic appliancefor effecting a seal between a sleeve engaged with the fenestration andthe shelf.
 18. The therapeutic appliance of claim 12, furthercomprising: an expandable bladder configured to be interposed betweenthe therapeutic appliance and a sleeve engaged with the fenestration,the expandable bladder for effecting a seal therebetween.
 19. Thetherapeutic appliance of claim 12, wherein the outer barrel of thetherapeutic appliance is encircled by at least one ring that isconfigured to mate with and engage a corresponding groove of a sleeveengaged with the fenestration.
 20. The therapeutic appliance of claim12, wherein the inner barrel of the therapeutic appliance is encircledby at least one ring that is configured to mate with and engage acorresponding groove of a sleeve engaged with the fenestration.
 21. Atherapeutic appliance configured to be implanted into a correspondinglyshaped fenestration in a wall of a cochlea, the therapeutic appliancecomprising: an outer barrel configured to be disposed distally from aninner section of the cochlea, the outer barrel having an outer barreldiameter dimension along a longitudinal axis; and an inner barrelconfigured to be disposed proximally to the inner section of the cochleain communication with the scala tympani region of the cochlea, the innerbarrel aligned coaxial with and adjacent to the outer barrel along thelongitudinal axis such that the inner barrel extends away from the outerbarrel, the inner barrel having an inner barrel diameter dimension aboutthe longitudinal axis, wherein the inner barrel diameter dimension issmaller than the outer barrel diameter dimension.
 22. The therapeuticappliance of claim 21, wherein the therapeutic appliance includes amicroactuator.
 23. The therapeutic appliance of claim 21, wherein thetherapeutic appliance includes a micropump.
 24. The therapeuticappliance of claim 21, wherein the outer barrel and the inner barrel arerespectively encircled by at least one ring of pliable material.
 25. Thetherapeutic appliance of claim 21, further comprising: a biocompatibleelastomeric coating disposed on an outer surface of the therapeuticappliance, the coating for effecting a seal between the outer surface ofthe therapeutic appliance and the fenestration in the wall.
 26. Thetherapeutic appliance of claim 21, further comprising: an O-ringdisposed on an outer surface of the therapeutic appliance for effectinga seal between the fenestration in the wall and the therapeuticappliance.
 27. The therapeutic appliance of claim 21, furthercomprising: an expandable bladder configured to be interposed betweenthe therapeutic appliance and a sleeve positioned between thefenestration and the therapeutic appliance for effecting a sealtherebetween.
 28. The therapeutic appliance of claim 21, wherein theouter barrel of the therapeutic appliance is encircled by at least onering that is configured to mate with and engage a corresponding grooveof a sleeve.
 29. The therapeutic appliance of claim 21, wherein theinner barrel of the therapeutic appliance is encircled by at least onering that is configured to mate with and engage a corresponding grooveof a sleeve.
 30. The therapeutic appliance of claim 21, furthercomprising: a shelf positioned between the inner and outer barrelshaving a length dimension along the longitudinal axis, the shelf havinga shelf diameter dimension, wherein the shelf diameter dimension issmaller than the outer barrel diameter dimension and larger than theinner barrel diameter dimension.
 31. A unitary initial fenestration burrconfigured for use in conjunction with a microdrill in forming acylindrically-shaped fenestration through a wall of a cochlea of asubject, the fenestration including an outer section that is called awell and an inner section which is smaller in diameter than the outersection, the fenestration also including an annularly-shaped well floorthat spans between one edge of the outer section of the fenestration andone edge of the inner section thereof, the initial fenestration burrcomprising: an elongated shaft one end of which is configured to besecured to the microdrill for rotating the initial fenestration burrduring use thereof in forming the fenestration; a cutting burr that islocated at a distal end of the shaft furthest from the microdrill duringuse of the initial fenestration burr in forming the fenestration; acylindrically-shaped outer section polishing burr that is located alongthe shaft near the cutting burr and which, during use of the initialfenestration burr in forming the fenestration, forms the outer sectionthereof, the outer section polishing burr having a diameter that islarger in a direction orthogonal to the shaft than a diameter of thecutting burr in a direction orthogonal to the shaft; and a washer-shapedinitial burr collar that is larger in diameter in a direction orthogonalto the shaft than a diameter of the outer section polishing burr in adirection orthogonal to the shaft, located along the shaft juxtaposedwith a side of the outer section polishing burr that is furthest fromthe cutting burr, and configured to contact an outer surface of the wallof the cochlea during use of the initial fenestration burr in formingthe fenestration to thereby limit penetration of the initialfenestration burr into the wall of the cochlea.
 32. The initialfenestration burr of claim 31, wherein the cutting burr has a diameterin a direction orthogonal to the shaft that does not exceed 1.4 mm. 33.The initial fenestration burr of claim 31, wherein the outer sectionpolishing burr has a diameter in a direction orthogonal to the shaftthat does not exceed 1.8 mm.
 34. The initial fenestration burr of claim31, wherein the outer section polishing burr is located 0.5 mm from thecutting burr along the shaft.
 35. The initial fenestration burr of claim31, wherein the outer section polishing burr is located 0.5 mm from thecutting burr along the shaft and extends 0.5 mm along the shaft.
 36. Theinitial fenestration burr of claim 31, wherein the outer sectionpolishing burr is diamond studded.
 37. The initial fenestration burr ofclaim 31, wherein the initial burr collar has a diameter in a directionorthogonal to the shaft that does not exceed 2.0 mm.
 38. The initialfenestration burr of claim 31, wherein: the cutting burr has a diameterin a direction orthogonal to the shaft that does not exceed 1.4 mm; theouter section polishing burr has a diameter in a direction orthogonal tothe shaft that does not exceed 1.8 mm, is located 0.5 mm from thecutting burr along the shaft, extends 0.5 mm along the shaft, and isdiamond studded; and the initial burr collar has a diameter in adirection orthogonal to the shaft that does not exceed 2.0 mm.
 39. Aunitary fenestration polishing burr configured for use in conjunctionwith a microdrill in forming a cylindrically-shaped fenestration througha wall of a cochlea of a subject, the fenestration including an outersection that is called a well and an inner section which is smaller indiameter than the outer section, the fenestration also including anannularly-shaped well floor that spans between one edge of the outersection of the fenestration and one edge of the inner section thereof,the fenestration polishing burr comprising: an elongated shaft one endof which is configured to be secured to the microdrill for rotating thefenestration polishing burr during use thereof in forming thefenestration; an inner section polishing burr that is located at adistal end of the shaft furthest from the microdrill during use of thefenestration polishing burr in forming the fenestration; and awasher-shaped polishing burr collar that has a diameter in a directionorthogonal to the shaft which is larger than a diameter of the innersection polishing burr in a direction orthogonal to the shaft and doesnot exceed a diameter of the outer section of the fenestration in adirection orthogonal to the shaft, is located along the shaft a shortdistance from the inner section polishing burr, and is configured tocontact the well floor of the well during use of the inner sectionpolishing burr in forming the fenestration to thereby limit penetrationof the fenestration polishing burr into the wall of the cochlea.
 40. Thefenestration polishing burr of claim 39, wherein the diameter of thepolishing burr collar in a direction orthogonal to the shaft is the sameas the diameter of the outer section of the fenestration in a directionorthogonal to the shaft.
 41. The fenestration polishing burr of claim39, wherein the diameter of the polishing burr collar in a directionorthogonal to the shaft does not exceed 1.8 mm.
 42. A unitaryouter-section grooving burr configured for use in conjunction with amicrodrill for forming an outer fenestration section groove thatencircles an outer section, that is called a well, of acylindrically-shaped fenestration that pierces a wall of a cochlea of asubject; the fenestration further including an inner section which issmaller in diameter than the outer section thereof, the fenestrationalso including an annularly-shaped well floor that spans between oneedge of the outer section of the fenestration and one edge of the innersection thereof, the outer-section grooving burr comprising: anelongated outer section grooving shaft one end of which is configured tobe secured to the microdrill for rotating the outer-section groovingburr during use thereof for forming the outer fenestration sectiongroove; a washer-shaped outer fenestration groove collar that is locatedat a distal end of the shaft furthest from the microdrill for contactingthe well floor during use of the outer-section grooving burr for formingthe outer fenestration section groove to thereby locate the outerfenestration section groove at a precise distance above the well floor,the outer fenestration groove collar having a diameter that is largerthan a diameter of the inner section and smaller than a diameter of theouter section; and an outer section groove cutting wheel that has adiameter in a direction orthogonal to the shaft which is larger than adiameter of the outer fenestration groove collar in a directionorthogonal to the shaft and does not exceed a diameter of the outersection of the fenestration in a direction orthogonal to the shaft andis located along the outer section grooving shaft a short distance fromthe outer fenestration groove collar.
 43. The outer-section groovingburr of claim 42, wherein the diameter of the outer section groovecutting wheel does not exceed 1.8 mm.
 44. A unitary inner-sectiongrooving burr configured for use in conjunction with a microdrill forforming an inner fenestration section groove that encircles an innersection of a cylindrically-shaped fenestration that pierces a wall of acochlea of a subject, the fenestration further including an outersection, that is called a well, which is larger in diameter than theinner section thereof, the fenestration also including anannularly-shaped well floor that spans between one edge of the outersection of the fenestration and one, edge of the inner section thereof,the inner-section grooving burr comprising: an elongated inner sectiongrooving shaft one end of which is configured to be secured to themicrodrill for rotating the inner-section grooving burr during usethereof for forming the inner fenestration section groove; an innersection groove cutting wheel that has a diameter in a directionorthogonal to the shaft which does not exceed a diameter of the innersection of the fenestration and is located at a distal end of the shaftfurthest from the microdrill; and a washer-shaped inner fenestrationgroove collar having a diameter that is larger than a diameter of theinner section and smaller than a diameter of the outer section and thatis located along the inner section grooving shaft a short distance fromthe inner section groove cutting wheel for contacting the well floorduring use of the inner-section grooving burr for forming the innerfenestration section groove to thereby locate the inner fenestrationsection groove at a precise distance below the well floor.
 45. Theinner-section grooving burr of claim 44, wherein the diameter of theinner section groove cutting wheel does not exceed 1.4 mm.
 46. Asequence of unitary fenestration polishing burrs configured for use inconjunction with a microdrill in forming a cylindrically-shapedfenestration through a wall of a cochlea of a subject, the fenestrationincluding an outer section that is called a well and an inner sectionwhich is smaller in diameter than the outer section, the fenestrationalso including an annularly-shaped well floor that spans between oneedge of the outer section of the fenestration and one edge of the innersection thereof, each of the fenestration polishing burrs in thesequence comprising: an elongated shaft one end of which is configuredto be secured to the microdrill for rotating the fenestration polishingburr during use thereof in forming the fenestration; an inner sectionpolishing burr that is located at a distal end of the shaft furthestfrom the microdrill during use of the fenestration polishing burr informing the fenestration; and a washer-shaped polishing burr collar thathas a diameter in a direction orthogonal to the shaft which is largerthan a diameter of the inner section polishing burr in a directionorthogonal to the shaft and does not exceed a diameter of the outersection of the fenestration in a direction orthogonal to the shaft; islocated along the shaft a short distance from the inner sectionpolishing burr; and is configured to contact the well floor of the wellduring use of the inner section polishing burr in forming thefenestration to thereby limit penetration of the fenestration polishingburr into the wall of the cochlea; and wherein the distance between thepolishing burr collar and a distal end of the inner section polishingburr is increased progressively for each successive fenestrationpolishing burr in the sequence of fenestration polishing burrs.
 47. Thesequence of fenestration polishing burrs of claim 46, wherein thediameter of the polishing burr collar in a direction orthogonal to theshaft for each successive fenestration polishing burr in the sequence offenestration polishing burrs is the same as the diameter of the outersection of the fenestration in a direction orthogonal to the shaft. 48.The sequence of fenestration polishing burrs of claim 46, wherein thediameter of the polishing burr collar in a direction orthogonal to theshaft for each successive fenestration polishing burr in the sequence offenestration polishing burrs does not exceed 1.8 mm.
 49. The sequence offenestration polishing burrs of claim 46, wherein: there are five (5)fenestration polishing burrs in the sequence of fenestration polishingburrs; a shortest distance between the polishing burr collar and adistal end of the inner section polishing burr of one of thefenestration polishing burrs is 0.75 mm; and the distance between thepolishing burr collar and a distal end of the inner section polishingburr for other fenestration polishing burrs in the sequence offenestration polishing burrs progressively increases: from 0.75 mm to1.00 mm; from 1.00 mm to 1.25 mm; from 1.25 mm to 1.50 mm; and from 1.50mm to 1.75 mm.
 50. A set of fenestration burrs configured for use inconjunction with a microdrill in forming a cylindrically-shapedfenestration through a wall of a cochlea of a subject, the fenestrationincluding an outer section that is called a well and an inner sectionwhich is smaller in diameter than the outer section, the fenestrationalso including an annularly-shaped well floor that spans between oneedge of the outer section of the fenestration and one edge of the innersection thereof, the initial fenestration burr comprising: a unitaryinitial fenestration burr that includes an elongated initial burr shaftone end of which is configured to be secured to the microdrill forrotating the initial fenestration burr during use thereof in forming thefenestration, a cutting burr that is located at a distal end of theinitial burr shaft furthest from the microdrill during use of theinitial fenestration burr in forming the fenestration, acylindrically-shaped outer section polishing burr that is located alongthe initial burr shaft near the cutting burr and which, during use ofthe initial fenestration burr in forming the fenestration, forms theouter section thereof, the outer section polishing burr having adiameter that is larger in a direction orthogonal to the initial burrshaft than a diameter of the cutting burr in a direction orthogonal tothe initial burr shaft, and a washer-shaped initial burr collar that islarger in diameter in a direction orthogonal to the initial burr shaftthan a diameter of the outer section polishing burr in a directionorthogonal to the initial burr shaft, located along the initial burrshaft juxtaposed with a side of the outer section polishing burr that isfurthest from the cutting burr, and configured to contact an outersurface of the wall of the cochlea during use of the initialfenestration burr in forming the fenestration to thereby limitpenetration of the initial fenestration burr into the wall of thecochlea; and a sequence of unitary fenestration polishing burrs, each ofthe fenestration polishing burrs in the sequence including an elongatedpolishing burr shaft one end of which is configured to be secured to themicrodrill for rotating the fenestration polishing burr during usethereof in forming the fenestration, an inner section polishing burrthat is located at a distal end of the polishing burr shaft furthestfrom the microdrill during use of the fenestration polishing burr informing the fenestration, and a washer-shaped polishing burr collar thathas a diameter in a direction orthogonal to the polishing burr shaftwhich is larger than a diameter of the inner section polishing burr in adirection orthogonal to the polishing burr shaft and does not exceed adiameter of the outer section of the fenestration in a directionorthogonal to the polishing burr shaft, is located along the polishingburr shaft a short distance from the inner section polishing burr, andis configured to contact the well floor of the well during use of theinner section polishing burr in forming the fenestration to therebylimit penetration of the fenestration polishing burr into the wall ofthe cochlea; and wherein the distance between the polishing burr collarand a distal end of the inner section polishing burr is increasedprogressively for each successive fenestration polishing burr in thesequence of fenestration polishing burrs.
 51. The set of fenestrationburrs of claim 50, wherein the cutting burr of the initial fenestrationburr has a diameter in a direction orthogonal to the shaft that does notexceed 1.4 mm.
 52. The set of fenestration burrs of claim 50, whereinthe outer section polishing burr of the initial fenestration burr has adiameter in a direction orthogonal to the shaft that does not exceed 1.8mm.
 53. The set of fenestration burrs of claim 50, wherein the outersection polishing burr of the initial fenestration burr is located 0.5mm from the cutting burr along the shaft.
 54. The set of fenestrationburrs of claim 50, wherein the outer section polishing burr of theinitial fenestration burr is located 0.5 mm from the cutting burr alongthe shaft and extends 0.5 mm along the shaft.
 55. The set offenestration burrs of claim 50, wherein the outer section polishing burrof the initial fenestration burr is diamond studded.
 56. The set offenestration burrs of claim 50, wherein the initial burr collar of theinitial fenestration burr has a diameter in a direction orthogonal tothe shaft that does not exceed 2.0 mm.
 57. The set of fenestration burrsof claim 50, wherein: the cutting burr of the initial fenestration burrhas a diameter in a direction orthogonal to the shaft that does notexceed 1.4 mm; the outer section polishing burr of the initialfenestration burr has a diameter in a direction orthogonal to the shaftthat does not exceed 1.8 mm, is located 0.5 mm from the cutting burralong the shaft, extends 0.5 mm along the shaft, and is diamond studded;and the initial burr collar of the initial fenestration burr has adiameter in a direction orthogonal to the shaft that does not exceed 2.0mm.
 58. The set of fenestration burrs of claim 50, wherein the diameterof the polishing burr collar of each fenestration polishing burr in thesequence of fenestration polishing burrs in a direction orthogonal tothe shaft is the same as the diameter of the outer section of thefenestration in a direction orthogonal to the shaft.
 59. The set offenestration burrs of claim 50, wherein the diameter of the polishingburr collar of each fenestration polishing burr in the sequence offenestration polishing burrs in a direction orthogonal to the shaft doesnot exceed 1.8 mm.
 60. The sequence of fenestration polishing burrs ofclaim 50, wherein: there are five (5) fenestration polishing burrs inthe sequence of fenestration polishing burrs; a shortest distancebetween the polishing burr collar and a distal end of the inner sectionpolishing burr of one of the fenestration polishing burrs is 0.75 mm;and the distance between the polishing burr collar and a distal end ofthe inner section polishing burr for other fenestration polishing burrsin the sequence of fenestration polishing burrs progressively increases:from 0.75 mm to 1.00 mm; from 1.00 mm to 1.25 mm; from 1.25 mm to 1.50mm; and from 1.50 mm to 1.75 mm.
 61. The set of fenestration burrs ofclaim 50, further comprising: a unitary outer-section grooving burrconfigured for use in conjunction with a microdrill for forming an outerfenestration section groove that encircles the outer section of thefenestration, the outer-section grooving burr comprising: an elongatedouter section grooving shaft one end of which is configured to besecured to the microdrill for rotating the outer-section grooving burrduring use thereof for forming the outer fenestration section groove; awasher-shaped outer fenestration groove collar that is located at adistal end of the shaft furthest from the microdrill for contacting thewell floor during use of the outer-section grooving burr for forming theouter fenestration section groove to thereby locate the outerfenestration section groove at a precise distance above the well floor,the outer fenestration groove collar having a diameter that is largerthan a diameter of the inner section and smaller than a diameter of theouter section; and an outer section groove cutting wheel that has adiameter in a direction orthogonal to the shaft which is larger than adiameter of the outer fenestration groove collar in a directionorthogonal to the shaft and does not exceed a diameter of the outersection of the fenestration in a direction orthogonal to the shaft, andis located along the outer section grooving shaft a short distance fromthe outer fenestration groove collar.
 62. The outer-section groovingburr of claim 61, wherein the diameter of the outer section groovecutting wheel does not exceed 1.8 mm.
 63. The set of fenestration burrsof claim 50, further comprising: a unitary inner-section grooving burrconfigured for use in conjunction with a microdrill for forming an innerfenestration section groove that encircles the inner section of thefenestration that pierces the cochlea, the inner-section grooving burrcomprising: an elongated inner section grooving shaft one end of whichis configured to be secured to the microdrill for rotating theinner-section grooving burr during use thereof for forming the innerfenestration section groove; an inner section groove cutting wheel thathas a diameter in a direction orthogonal to the shaft which does notexceed a diameter of the inner section of the fenestration and islocated at a distal end of the shaft furthest from the microdrill; and awasher-shaped inner fenestration groove collar having a diameter that islarger than a diameter of the inner section and smaller than a diameterof the outer section and that is located along the inner sectiongrooving shaft a short distance from the inner section groove cuttingwheel for contacting the well floor during use of the inner-sectiongrooving burr for forming the inner fenestration section groove tothereby locate the inner fenestration section groove at a precisedistance below the well floor.